White LED Set-up Converter

EC4501

Page 7 of 10

3F27N-Rev.P001

Typical Application Circuit

OPERATION DESCRIPTION

The EC4501 uses a constant frequency, peak current mode boost regulator architecture to regulate the series string of

white LEDs. The operation of the EC4501 can be

understood

by

referring

to

the

simplified

block diagram

shown above. At the start of each oscillator cycle, the control logic turns on the power switch M1. The

signal

at

the

non

‐inverting input of the PWM comparator is proportional to the switch current, summed together with a portion

of the oscillator ramp When this signal reaches the level set by the output of error amplifier, the PWM comparator resets the

latch in the control logic and turns off the power switch. In this manner, error amplifier sets the correct peak current level

to keep the LED current in regulation. If the feedback voltage starts to drop, the output of the error amplifier increases.

This results in more current to flow through M1, hence increasing the power delivered to the output.